CJC H1 CHEM P2 Prelim

8872/02/CJC Prelim 09 1 Name Class: 2T CATHOLIC JUNIOR COLLEGE CHEMISTRY 8872/02 Higher 1 Paper 2 Preliminary Examination 2009 2 hours Candidates answer Section A on the Question Paper and Section B on separate paper. Additional Materials: Paper Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use paper clips, highlighters, glue or correction fluid. Section A Answer all questions. Section B Answer any two questions on separate answer paper. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A B5 B6 B7 Total There are a total of 10 printed pages including this cover page.

8872/02/CJC Prelim 09 2 Section A Answer all the questions in this section in the spaces provided. 1 (a) The decomposition of hydrogen peroxide is a first order reaction. H 2O2 H 2O + ½O 2 The activation energy of the forward reaction is 1 80 kJ mol -1 and that for the reverse reaction is 282 kJ mol -1. The rate of the reaction can be increased by the addition of platinum catalyst. (i) Use the data provided to construct a reaction p athway diagram for the uncatalysed reaction, indicating the activation energy of the forward reaction. (ii) Calculate the enthalpy change for the decompos ition of hydrogen peroxide. ΔH = __________________ (iii) State how the reaction pathway diagram will c hange with the addition of platinum catalyst. (iv) Use the bond energies given in the Data Booklet to calculate another value for the enthalpy change for the decomposition of hydrogen peroxide. (The structure of H 2O2 can be taken as: H-O-O-H) (v) Suggest a reason for the discrepancy between th e values in (a) (ii) and that in (a)(iv). [7]

8872/02/CJC Prelim 09 3 (b) Wine contains a small amount of sulfur dioxide that is added as a preservative. The sulfur dioxide content of the wine can be determined by the following method. A 50 cm 3 sample of wine is reacted with 40 cm 3 of 0.01 mol dm -3 of aqueous iodine which is present in excess. The unreacted iodine requires 23.60 cm 3 of 0.02 mol dm -3 sodium thiosulfate, Na 2S2O3 for complete reaction. This reaction follows the equation given: I2 + 2S 2O3 2- /barb2right S 4O6 2- + 2 I - (i) What is the amount of unreacted iodine that re acted with sodium thiosulfate? (ii) What is the amount of iodine that reacted with sulfur dioxide in the sample of wine? (iii) The sulfur dioxide in the wine is oxidised b y I2 to sulfate, SO 4 2-, according to the half equation: SO 2 + 2H 2O /barb2right SO 4 2- + 4H + + 2e - With reference to the Data Booklet , construct a balanced equation for the reaction between SO 2 and I2. Hence, find the amount of sulfur dioxide present in the wine. (iv) Determine the concentration of sulfur dioxide , in mol dm -3, in the wine. [5] [Total: 12]

8872/02/CJC Prelim 09 4 2 The following diagram represents the first ionisation energies of the elements in Period 2 and in Period 3 of the Periodic Table. (a) (i) Define the term first ionisation energy . (ii) Give an equation that represents the first ion isation energy of Be. [2] (b) Account for the fact that the first ionisation ene rgy of O is less than that of N. [2] (c) On the graph below, sketch the first six successiv e ionisation energies of C. [2] (d) (i) SiO 2 has a melting point of 1650 oC, but SiCl 4 melts at -70 oC. Account for the difference in melting point in terms of structure and bonding. (ii) Write an equation for the hydrolysis of SiCl 4 and state the pH of the resulting solution. [4] [Total: 10] Ionisation energy / arbitrary units Ionisation number

8872/02/CJC Prelim 09 5 3(a) Complete the reaction scheme below by writing t he structural formula of the products A – D in the spaces provided. Give the reagents and conditions for the reactions E and F. E : F : [6] E F Excess conc. H 2SO 4 170 oC LiAlH 4 in dry ether OH CH 2Cl KMnO 4 (aq), dil H 2SO 4, reflux OH CN CH 2Cl OH CO 2H CH 2Cl A B C D Alcoholic NH 3, heat in sealed tube

8872/02/CJC Prelim 09 6 (b) Three compounds J, K and L are given below: J K L Describe briefly how you would positively identify the three compounds using simple chemical tests. [3] (c) Give the reagents, conditions and intermediates to synthesise 3-chlorobenzoic acid from methylbenzene. (Note that the synthesis requires more than one st ep.) [3] [Total: 12] CH 3 CO2H Cl methylbenzene 3-chlorobenzoic ac id CH=CH 2 CH 2CHO CH(CH 3)OH

8872/02/CJC Prelim 09 7 4. In the Age of Exploration, scurvy was a very seriou s problem among sailors. This resulted in their high death tolls. Sufferers of this disease often appear pale, are likely to have spots on their skin s, and will also experience bleeding. When vitamin C was introduced to the diet of these sailors in that era, their fatality rates dropped significantly. Vitamin C has the following structure: In more recent times, vitamin C can be synthesised in the laboratory that involves biological and organic chemistry. A global health-care company fr om Switzerland called Hoffmann-LaRouche was the first to manufacture vitamin C synthetically from glucose. Vitamin C tablets are now readily available in the market. The common doses are 100 mg, 250 mg, 500 mg and 1000 mg tablets. These tablets can come in chewable form or in effervescent form. The amount of vitamin C in a tablet can be determin ed by titration with a complex of iodine called triiodide. The soluble triiodide is formed when the relatively insoluble iodine is present in a solution of iodid e ions: I2 + I- I3 - Triiodide oxidises vitamin C (C 6H8O6) to form dehydroascorbic acid: C6H8O6 + I3 - + H 2O /barb2right C 6H6O6 + 3 I- + 2H + Howevever, when the all the vitamin C is oxidised, iodine and triiodide will be present, which react with starch to form a blue-black complex. The blue-black color is the endpoint of the titration. (a) Suggest a possible method by which the sailors man aged to introduce vitamin C into their diets. [1] (b) On the Vitamin C structure given above, circle the functional group that can be easily oxidised to form a carboxylic acid group. [1] (c) Based on the description given in the above passag e, what is the indicator used for the titration? [1] (d) A vitamin C tablet is crushed and made into a 100 cm 3 solution. 25.0 cm 3 of the vitamin C solution was titrated with 22.60 cm 3 of 0.031 mol dm -3 triiodide solution. Which of the four common doses of vitamin C di